This invention relates to electrostatic copying machines, in which a latent electrostatic image is developed with developer particles and transferred to a sheet or web of support material.
Many coping machines have provided automatic devices for replenishing the developer material so that the standard of development of the images will not decrease while the machine is being used. This automatic replenishment has usually taken place at intervals while the machine is in operation, although more sophisticated machines such as that described in British patent specification No. 1 186 775 only replenish the developer material when its density is sensed by optical means to have fallen below a predetermined value.
The simple form of developer replenishment, which operates while the machine is in operation suffers from the disadvantage that the machine is in operation for a shorter time per copy produced when multiple copies of a single original are being made, than when a single copy of an original is being made because the time taken in starting up the machine and shutting it down before and after a copying run only occurs once, no matter how many copies are made during the run. If the developer replenishment is set to provide enough developer during the production of multiple copies of a single original, single copies made will tend to be over-developed since the machine will be in operation longer per copy during this mode of operation.